The intervertebral discs act as cushions between vertebral bodies. Intervertebral discs comprise cartilaginous endplates, made up of 55% water, 8% proteoglycan, and 25% collagen, nucleus pulposus, made up of 77% water, 14% proteoglycan, and 4% collagen, and annulus fibrosus, made up of 70% water, 5% proteoglycan, and 15% collagen.
As discs age, degeneration occurs. The disc loses height causing pressure on the spinal cord and/or nerves which leads to pain, loss of osmotic pressure in the nucleus, tearing in the annulus, and nuclear material to leak out of the outer rim of the annulus.
Patients whose symptoms do not improve with medications and non-operative treatments such as physical therapy, and patients with severe spinal deformity, instability, or end-stage arthritis are definitively managed with surgery to cause the vertebrae of the spine to weld together, in a procedure called fusion. Spine fusion eliminates motion between the vertebrae, by allowing bone bridges to form between them. Over 400,000 patients undergo spinal fusion each year (Coe et al. (2006); Ong et al. (2007); Rajaee et al. (2012)).
This bony-bridging and fusion is accomplished using surgeries that can last several hours, and have high rates of associated complications, pain and suffering, and high costs (both from care delivered and lost days at work). Additionally, in greater of 20% of the surgeries, there is a failure to relieve lower back pain symptoms. In approximately 5 to 10% of surgeries, there is a failure of fusion known as pseudarthrosis. There is also a risk of excessive blood loss, infection, pain at the graft site, graft rejection, blood clots, and nerve injury.
A better method to produce spine fusions is needed, which would allow spine fusions to be created more economically, with less risk to the patient, and less cost to society.